In the manufacture of semiconductor devices, such as integrated circuits (ICs), dynamic random access memories (DRAMs), etc., large thin wafers (typically of silicon) from which the semiconductor devices are fabricated must frequently be transferred from one processing chamber to another. This transfer of wafers must be carried out in a clean environment and often at sub-atmospheric pressures. To this end various mechanical arrangements have been devised for transferring wafers to and from processing chambers in a piece of equipment or from one piece of equipment to another.
It is the usual practice to load wafers into a cassette so that a number of wafers can be carried under clean-room conditions safely and efficiently from one place to another. A cassette loaded with wafers may then be inserted into an input/output (I/O) chamber (“load lock” chamber) where a desired gas pressure and atmosphere can be established. The wafers are fed one-by-one to or from their respective cassettes into or out of the I/O chamber.
It is desirable from the standpoint of efficiency in handling of the wafers that the I/O chamber be located in close proximity to a number of processing chambers to permit more than one wafer to be processed nearby and at the same time. To this end two or more chambers are arranged at locations on the periphery of a transfer chamber which is hermetically sealable and which communicates with both the I/O chamber and the processing chambers. Located within the transfer chamber is an automatically controlled wafer handling mechanism, or robot, which takes wafers supplied from the I/O chamber and then transfers each wafer into a selected processing chamber. After processing in one chamber a wafer is withdrawn from the chamber by the robot and inserted into another processing chamber, or returned to the I/O chamber and ultimately a respective cassette.
Semiconductor wafers are by their nature fragile and easily chipped or scratched. Therefore they are handled with great care to prevent damage. The robot mechanism which handles a wafer holds it securely, yet without scratching a surface or chipping an edge of the brittle wafers. The robot moves the wafer smoothly without vibration or sudden stops or jerks. Vibration of the robot can cause abrasion between a robot blade holding a wafer and a surface of the wafer. The “dust” or abraded particles of the wafer caused by such vibration can in turn cause surface contamination of other wafers. As a result, the design of a robot requires careful measures to insure that the movable parts of the robot operate smoothly without lost motion or play, with the requisite gentleness in holding a wafer, yet be able to move the wafer quickly and accurately between locations.
Because of space constraints under and/or within a transfer chamber, it is desirable to reduce the height of the motor assembly employed to drive a robot. It is also desirable to provide a robot able to independently handle multiple wafers so as to increase the through-put of a wafer-processing apparatus.